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A series of imide‐based small molecules, namely NA, NAA, and NEA with simple structures, were designed and synthesized by introducing different amine side‐chains into the benzene unit of imide, which were used as cathode interfacial materials in organic solar cells (OSCs). The amine side‐chain substitution positions were systematically investigated with these small‐molecule imides. Compared with NA without amide chains‐NAA, and NEA, with 3‐dimethylaminopropylamine and ethylenediamine chains, respectively‐show bathochromic shifts in absorption, decreased band gaps, and higher highest occupied molecular orbital (HOMO) energy levels. A power conversion efficiency (PCE) of 15.04 % was obtained with the NEA‐based as‐cast OSCs with a high open‐circuit voltage and fill factor for PM6 : Y6 blend and the maximum PCE of 15.80 % was reached for as‐cast PM6 : Y6 : IT‐M ternary OSCs. NEA exhibits better conductivity, higher electron mobility, and stronger the capability of lower work function of cathode among three molecules, affording OSCs with better photovoltaic performance. Additionally, these three molecules show excellent thermal stability both in solution and in films at 150 °C. The results indicate that imide‐based small molecules are promising cathode interfacial materials for commercial OSCs. [ABSTRACT FROM AUTHOR]

A new organic small molecule, DCA3TBDF, with a 2D benzo[1,2-b:4,5-b']difuran (BDF) moiety as the central core and octyl cyanoacetate units as the end-capped blocks, was designed and synthesized for solution-processed bulk heterojunction solar cells. DCA3TBDF possesses good solubility in common organic solvents such as toluene, CH2Cl2, chlorobenzene, and CHCl3 and good thermal stability with an onset decomposition temperature with 5% weight-loss occurring at 361 °C. The DCA3TBDF thin film showed a broad absorption at λ=320-700 nm and high crystallinity. Small-molecule organic solar cells based on DCA3TBDF and [6,6]- phenyl-C61-butyric acid methyl ester demonstrated promising power conversion efficiency with a high fill factor under the illumination of AM 1.5G (100 mWcm-2). [ABSTRACT FROM AUTHOR]

At present, high-performance small molecule donors for organic solar cells (OSCs) are almost entirely composed of the electron donating core benzodithiophene (BDT), which has resulted in a lack of material diversity and further improvement. In this article, we constructed an A-π-A′-π-A conjugated structure using electron withdrawing group benzobisthiazole (BBT) core and rhodanine end group, and synthesized two small molecule donors BBTSM-3 and BBTSM-4. Under the dual electron withdrawing effects of BBT and rhodanine, the HOMO energy levels of BBTSM-3 and BBTSM-4 reached extremely low levels (−5.60 eV and −5.64 eV), but still matched well with the acceptor Y6. In addition, through reasonable side chain regulation, BBTSM-3 exhibited stronger crystallinity and weaker aggregation at the same time. This provides a reference point for the use of the electron withdrawing core and the regulation of side chains among small molecule donors. Benzobisthiazole and rhodanine construct small molecule donors with A-π-A′-π-A molecular charge transport system and really low HOMO energy levels. [Display omitted] • Benzobisthiazole and rhodanine were used to synthesize small molecule donors with A-π-A′-π-A system. • BBTSM reached really low HOMO energy levels, while still exhibited good exciton dissociation with Y6. • Stronger crystallinity and weaker aggregation can be achieved simultaneously by regulating the side chains. [ABSTRACT FROM AUTHOR]

Energy level regulation and crystallization optimization of materials are the key ideas to improve the performance of organic solar cells. In this work, based on clarifying small molecule structure, we introduce thiazole into different positions of π-bridge and investigate its effect on the properties of small molecule donors (SMDs) and related device performance. As thiazole gradually moves towards BDT, the electron clouds of these three SMDs (BTTTzR, BTTzTR and BTzTTR) tend to be divided on the framework, gradually deepened the energy level, and enlarged band gaps. In terms of device performance, the BTTzTR:Y6 device shows good inhibition of charge recombination and phase separation performance, and the efficiency of the related OSCs is 7.87 %. Morphological analysis shows that BTTTzR is prone to form nanoscale microcrystals after thermal annealing treatment, with slightly decreased performance of 6.79 %. BTzTTR is affected by difficult intramolecular charge transfer and weak intermolecular interactions, shows the worst performance of 5.77 %. This work is conducive to a deeper understanding of the electron-deficient substitution of the π-bridge in SMDs. [Display omitted] • Studied effect of thiazole position in π-bridge on the performance of SMDs. • Thiazole sequence results in different changes in crystallizations and energy levels. • Transfer of thiazole towards the center enhances acceptor properties. • Transfer of thiazole towards the end groups enhances molecular crystallization. [ABSTRACT FROM AUTHOR]

• 10–12% High power conversion efficiency is achieved by halogenated ITIC and BDT polymer. • Fluorinated, chlorinated and brominated ITIC acceptor all fit BDT-BDD backboned donor. • 70% FF are achieved by all halogenated ITIC based devices. Acceptor halogenation is an excellent modification method for modulating molecular energy levels, improving optical absorption, shortening the intermolecular packing distance thus ameliorating morphologies and achieving effective exciton dissociation and charge transfer of organic photovoltaic device. In this work, F, Cl and Br terminated ITIC small molecule acceptor (SMA) derivatives (IT-2F, IT-2Cl and IT-2Br) are designed and synthesized to compare the halogen substitution effect. Among these three acceptors, IT-2F based PSCs devices show the highest power conversion efficiencies (PCEs) around 12.08%, but Br terminated ITIC show downshifted LUMO energy level. Brominated ITIC show comparable PCEs with Cl and F terminated compound, and moreover chlorinated and brominated ITIC show low synthesis cost and easy purification than fluorinated materials, which may be favorable for future commercialization. [ABSTRACT FROM AUTHOR]

In organic solar cells (OSCs), it is very important to investigate the relationship between the structure and performance of materials by rational design of small molecule donors (SMDs). In this work, we use thiazole replace a thiophene unit in the π bridge, which could strengthen the connection between π bridges and end groups (EGs). Due to the N–S non-covalent interaction between EG and thiazole unit, the negative charge region of SMDs is expanded, the electron-withdrawing ability of EGs is also enhanced, and the corresponding molecular framework is twisted into a unique linear type. This can effectively enhance intermolecular interaction, promote molecular crystallization, and help to improve hole mobility of related SMDs. This work enriches design strategy that strengthens the interaction between π bridges and EGs, and provides a reference for studying the relationship between molecular structure and crystallinity. [Display omitted] • Thiophene π bridge in the small molecule donor is replaced by thiazole. • N–S interaction leads to linear conformation of conjugated skeleton. • Thiazole unit expand the negative electron distribution region of end groups. • N–S interaction improves hole mobility of small molecular donor. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electron withdrawing benzobisthiazole core unit was used to synthesize small molecule donors. • BBTSM-1 and BBTSM-2 adopted A-π-A'-π-A conjugated structures and had really low HOMO energy levels. • Careful regulation of side chains not only weakened molecular aggregation but also enhanced crystallinity. All-small-molecule (ASM) organic solar cells (OSCs) are in advantage of their defined molecular structures and good reproducibility. However, the state-of-art donor molecules are usually based on benzodithiophene (BDT) as the core unit, which limits the modulation of energy levels, optical absorption, and opto-electronic properties. In this research, we designed and synthesized two small molecular donors (BBTSM-1 and BBTSM-2) with electron withdrawing benzobisthiazole (BBT) as the core unit, developing a type of A-π-A'-π-A conjugated system. The molecules exhibit reduced energy levels, high charge carrier mobilities, and ordered edge-on molecular packing in thin films. High power conversion efficiency of 11.8% was achieved in solar cells based on BBTSM-1:Y6, which indicating that small molecular donors based on the weak electron withdrawing BBT unit would be promising candidates for high-performance organic solar cells. [ABSTRACT FROM AUTHOR]

In this work, we designed and synthesized two "A-π-A" structural small molecules based on N -dimethylaminopropyl-1,8-naphthalimide with π-bridge, namely 4,4'-(thiophene-2,5-diyl)bis(2-(3-(dimethylamino)propyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione) (ONTN) and 4,4'-(1,4-phenylene)bis(2-(3-(dimethylamino)propyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione) (ONBN), which are used as cathode interfacial materials (CIMs) to systematically reveal the effect of π-bridge of 1,8-naphthalimide-based cathode interlayers for efficient organic solar cells (OSCs). Compared with ONBN, ONTN shows higher decomposition temperature, more red-shift absorption, lower LUMO and higher HOMO energy levels, higher electron mobility and conductivity, and more uniform film morphology. Both molecules exhibit excellent thermal stability and high light transmittance. The OSCs based on ONTN with PBDB-T:ITIC as active layer demonstrate a power conversion efficiency (PCE) of 10.38%, higher than the control device of ONBN (a PCE of 9.04%). It turns out that thiophene π-bridge 1,8-naphthalimide-based ONTN got better performance as CIMs than that of ONBN with benzene π-bridge. [Display omitted] • We synthesize new building block 2-bromo-2-(3-(dimethylamino) propyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione and demonstrate its great potential for constructing cathode interfacial materials using in OSCs. • We find that thiophene π-bridge in ONTN significantly enhances the device efficiency. • We investigate effects of the π-bridge on electronic properties, charge transport, film morphology, and photovoltaic properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] Deep HOMO benzodithiophene (BDT) and benzotriazole based molecule is reported. [•] Solar cells show high Voc of 0.93V with PCEs of 3.61% device. [•] Solar cells also can show high FF of 72% with PCEs of 2.31% device. [ABSTRACT FROM AUTHOR]

Highlights: [•] Isoindigo-based compound is synthesized. [•] The solar cells device shows high open-circuit voltage of 1.0V. [•] Small molecule solar cells device is solution-processing. [ABSTRACT FROM AUTHOR]

[Display omitted] • All organic PC 71 BM/g-C 3 N 4 photocatalysts were constructed by in situ self-assembly. • The heterostructures possess satisfactory biocompatibility. • The PC 71 BM served as the electron acceptor and photosensitizer. • · O 2 - acted as the main active species in the degradation process. Photocatalysis has been reported as a potential water purification technology for combating the pathogenic bacteria and degrading the hazardous chemicals. The photoactive organic semiconductors as the emerging class of an alternative to the traditional developed inorganic semiconductors are being widely pursued due to their tunable structures and low toxicity. Herein, the all-organic [6,6] -phenyl C 71 butyric acid methyl ester (PC 71 BM)/g-C 3 N 4 heterostructure have been created by introducing self-assembled n-type fullerene small molecule to the g-C 3 N 4 surface in situ. The absorption edge of the heterostructures with PC 71 BM as the photosensitizer extend from 450 to 650 nm. Moreover, the charge separation and transfer efficiencies of the photocatalysts are greatly promoted even with 1.0% amount of PC 71 BM because of its low reorganization energy and high reduction potential. All of these superiorities endow the heterostructures with over 99.7% antibacterial rates toward E. coli and S. aureus and excellent performance against their biofilms after irradiation for 135 and 180 min, respectively. Additionally, the heterostructures achieve excellent photocatalytic degradation ability for Rhodamine B and tetracycline. Importantly, the in vitro experiments reveal that the as-prepared heterostructures possess satisfactory biocompatibility and their toxicity is negligible. This study provides a new perspective for designing ecofriendly all-organic heterostructures with high photocatalytic activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three small molecule donors based on asymmetric BDT core were synthesized. • Effects of side chains and ending groups on properties of donors were investigated. • 2D-2D asymmetric SMD3 ending capped by rhodanine showed best photovoltaic property. In this work, we employed symmetry-breaking strategy to construct A-π-D-π-A typed small molecule donors SMD1, SMD2 and SMD3 to reduce the self-aggregation in blends and form ideal phase separation morphology. The effect of different side chains and terminal groups on the photovoltaic properties of these asymmetric small molecule donors were investigated in detail. SMD3 shows more red-shifted absorption and weaker self-aggregation than SMD1 and SMD2. Consequently, SMD3:PC 71 BM blend films show homogenous morphology, which is beneficial for exciton dissociation and charge transport. As a result, SMD3:PC 71 BM based devices exhibit the highest power conversion efficiency (PCE) of 4.67%. Our investigation proved that the benzene-alkoxyl and thiophene-alkylthiol are ideal candidates for side chains on BDT and 3-isooctyl rhodanine is an ideal terminal group for asymmetric small molecular donors. [ABSTRACT FROM AUTHOR]

Multiple strategies have been developed to improve the photovoltaic performance of organic solar cells (OSCs) by fine-tuning the morphology of the active layers, such as introducing functional third components, taking post-treatments and so on. In this work, a series of non-volatile solid additives BT, BTOR, BT2F, BTNO 2 (2 + 6), and BTNO 2 (6) were synthesized, by introducing substituent groups into benzothiadiazole units, and the thermal stability, optical and electrochemical properties were systematically studied. These additives were applied to further investigate the effect on the photovoltaic performance of OSCs. The results show that these additives could effectively promote exciton dissociation and charge transfer, reduce bimolecular recombination, and optimize the morphology of the active layer. Significantly, the PBDB-T:ITIC-based devices processed with BT achieved a power conversion efficiency (PCE) of 11.57%, increased by 17% compared to the as-cast devices due to the high and balanced carrier mobility. Enhancement of PCE proved the feasibility of the application of non-volatile solid additives in the non-fullerene-based binary system. [Display omitted] • Construction of ladder like core structure with non-covalent interaction. • Solid additives were applied in enhancing photovoltaic performance of OSCs. • Introducting additives increased PCE of non-fullerene OSCs devices by 17%. [ABSTRACT FROM AUTHOR]